Hi,
you need to use the e-commerce functions in transformation to display the SKU data. Using default transformation you are displaying just document data.
I would like to recommend to check the Site Manager -> Development -> Document types ->
E-commerce - Transformations type -> Transformations tab. There are created some sample transformations. Or, you can also take a look on the sample E-commerce site template to see how the transformations are used and which controls and functions are displaying the data you want.
Best regards,
Juraj Ondrus